This invention relates to a test set for testing relay contact protection networks. In particular it relates to apparatus arranged for coupling the test set to various contact protection networks located in relay contact controlled circuits.
Typically, relay contacts are used in the field of communications to control transmission and switching circuits to establish communication paths between calling and called telephone stations. During operation, a relay contact closes and opens contact surfaces which result in abrupt changes in the electrical states appearing at the contact surfaces and lead to surges of voltage and current with associated breakdowns in the gap between the contact surfaces. These surges lead to localized heating at the contact surfaces and cause vaporization, welding, and brief high frequency oscillations in the contact controlled circuitry that sometimes cause external radiation interference and damage to wiring and components. The energy dissipated in the gap breakdown causes erosion of the contact metals which eventually wear through to poor conducting base metals upon which the contact metals have been plated. Erosion of the contact surfaces can also produce metallic bridges to short circuit contact surfaces and cause contacts to latch together so that they fail to separate.
There are many contact uses where the damage caused by voltage and current surges severely shortens the service life of the contact surface metal. Circuits controlled by the closing and opening of relay contacts are oftentimes modified by the addition of a contact protection network intended to protect the relay contact surfaces and thereby enable the contacts to serve their intended service life. The opening of an inductive circuit is the principal offender as to contact erosion, radiation interference, and gap breakdown damage to the high voltage surges. Contact protection networks comprise resistive, capacitive, and other linear and nonlinear elements, or combinations thereof, and are connected across relay coil windings located in contact controlled circuits to dissipate contact energy by limiting contact voltage and current.
Contact protection networks sometimes fail in service and thereby allow damage to occur to the unprotected contact surfaces. The unprotected contacts in turn fail and prevent proper operation of the relay in performing the task of controlling the circuit. The past procedure for testing contact protection networks has been to remove suspected networks from relay controlled circuits and connect them to a test bridge circuit that is operated to measure the value of the network. This procedure requires that a circuit suspected of having a defective contact protection network must be removed from service while each contact protection network is disconnected from across a relay coil winding, removed from the circuit, measured on a test bridge circuit and reconnected after testing to the circuit relay coil winding.
A need exists in the art for a test set arranged to allow rapid in-circuit testing of contact protection networks. A need also exists for apparatus arranged to selectively connect a test set to various relay coil winding configurations for the purpose of enabling the test set to be used to test various types of contact protection networks connected thereto.